High-performance sports cars currently feature four independent suspensions, which are normally of the “four-link” type for compactness and good road performance.
A four-link suspension connects a wheel hub to the car frame, and comprises a wheel hub supporting member connected mechanically to the car frame to move substantially vertically with respect to the frame.
Vertical movement of the supporting member is opposed by a spring-shock absorber assembly fixed on one side to the car frame, and connected mechanically on the other side to the supporting member by connecting means of given geometry.
The geometry of the connecting means determines a suspension ratio, which defines the ratio between vertical movement of the supporting member and a corresponding variation in the length of the spring-shock absorber assembly, and is either constant or variable along the travel of the spring-shock absorber assembly, depending on the geometry of the connecting means.
The response characteristics of the spring-shock absorber assembly are normally constant, and constitute a trade-off between optimum dynamic performance of the car and an adequate degree of passenger comfort.
In an attempt to adapt response of the spring-shock absorber assembly to current driving conditions, electronically controlled shock absorbers have been proposed to vary damping performance of the shock absorbers, and which provide for reduced damping in racing or extreme conditions (e.g. as when braking sharply) and increased damping in normal on-road driving conditions.
Suspension performance adjustment using electronically controlled shock absorbers, however, is limited, on account of failure to make any adjustment whatsoever in response of the springs. It has therefore been proposed to employ air springs, as opposed to conventional mechanical steel springs. By adjusting the internal pressure of an air spring, it is possible to adjust both the preload of the spring, and hence the height of the car, and the stiffness of the air spring.
Air springs, however, have several drawbacks as compared with conventional mechanical steel springs: they are more expensive, bulky, and less dependable, have a shorter working life, and, above all, are functionally inferior in a manner preventing use in high-performance sports cars. Moreover, the stiffness adjustment achieved by adjusting the internal pressure of an air spring is fairly limited, and depends anyway on the adjustment in height of the car.
DE19923343A1 disclose a vehicle with sprung wheels and with deflection between wheel stroke and damping or spring member stroke. The vehicle has wheels supported on at least one damping or spring member, which is held at one end in such a manner that the spacing between the bodywork and the wheel axle can be varied for different load conditions; there is a deflection between the wheel stroke and the stroke of the damping or spring member.